PENTAGON —
U.S. Defense Secretary Chuck Hagel says the United States is prepared to evacuate American citizens in the event of a terrorist attack at the upcoming winter Olympic games in Sochi. Russia has yet to accept the U.S. offers of security assistance, and the U.S. Navy is moving ahead with plans to send two warships to the Black Sea in the coming days.

The recent string of bombings in Russia is - for U.S. officials - a sign that the threat of an attack at the olympics is real.

The Pentagon has offered to send two U.S. Navy ships to the Black Sea, and U.S. and Russian officials have been in talks that have included the possible sharing of U.S. technology on improvised explosive devices.

The Russians have yet to accept any offers.

Meanwhile, U.S. commanders are making contingency plans to evacuate thousands of Americans in case there's an attack. Pentagon spokesman Rear Admiral John Kirby:

“The ships that we're going to be putting in the Black Sea are ships that have by design multiple capabilities, as most of our ships do. And most of our ships are capable of helicopter lift. Most of our ships have some sort of medical facility onboard," said Kirby.

The recent attacks and reports that a suspected female terrorist has been spotted in Sochi have fueled discussion in Washington about security.

Juan Zarate is a defense analyst at the Center for Strategic and International Studies.

“These aren’t just imaginings or sort of, you know, one-off threat threads that have to be chased down, as often the U.S. has to do. But this is a real terrorist threat that exposes athletes, sponsors, U.S. citizens that are going to attend the event.," said Zarate.

The Russians have offered assurances that they can handle security threats on their own, and the U.S. government is being careful not to embarrass Moscow. But analysts say U.S. officials are concerned they aren't getting the kind of close cooperation they have had with Olympic hosts in the past.

“The Russians have grown more and more concerned over the threat and are concerned over the perception of insecurity and therefore have not wanted to allow the United States and other security services in on the ground to assist," said Zarate.

U.S. officials have begun to speak openly about their concerns and have begun planning for a possible worst-case scenario.

That scenario would include pre-positioning ships as well as aircraft off the coast to move out wounded athletes and other U.S. citizens - if the worst occurs.